Peer-to-peer communication systems, such as local area networks (LANs), have become the technique of choice for connecting many computer devices, or stations, together. The basic architecture of a LAN allows multiple stations to vie for access, on an equal basis, to a physical media of a moderately high bandwidth. A key feature of the most popular LAN access methods, such as Carrier Sense Multiple Access with Collision Detection (CSMA/CD), Token-Passing Ring, and Token-Passing Bus, is that they do not require a central communication controller. The net result is a system which allows interconnecting a large number of stations simply, quickly, and without the need to purchase expensive interface hardware for each station.
Thus, the very power of a LAN lies in its ease of access to a shared media. However, simplicity of access to a shared media means that LANs have some well known security problems, including privacy and unauthorized access.
Privacy is a problem since every station can usually read every data packet transmitted. Thus, with the standard arrangement, there is no way to prevent an unauthorized user from connecting to the LAN and reading sensitive information.
Since any station can also obtain control of the media, and begin transmitting data messages, or packets, controlling unauthorized write access is also a problem, for several reasons.
First, an unauthorized user can seriously disrupt the orderly sharing of the LAN, simply by repeatedly transmitting packets, either intentionally or unintentionally.
Second, there are no built-in controls to limit access of stations with each other or with various LAN services, such as printers or disk drives. The net result is that there is no standardized way to prevent an authorized user from monopolizing shared resources.
Third, there is no mechanism for distributing the packet traffic in any controlled manner. In other words, because LANs inherently allow every station equal access, they also do not inherently afford any mechanism which allows some users a greater or lesser amount of service.
Conventional solutions to such LAN access control problems include encryption, operating system controls, and physical isolation.
Encryption has been the most popular LAN security solution. Encryption mechanisms have many different attributes, but generally fall into two categories. First, they are implemented such that network stations must participate, by having the required encryption hardware to provide a secure physical connection path from station to station. Alternately, encryption can be implemented as part of a communication protocol used by the stations. In this case, the actual data packets include encrypted primitives.
Another technique is to require the stations to follow some sort of security protocol. However, this has the disadvantage of requiring each station to be reprogrammed; the lack of widely accepted security protocols makes this approach cumbersome to implement.
Network operating system software, such as NetWare products marketed by Novelle, and the LAN Manager products marketed by Microsoft Corporation, can also limit access to the various network services they support. Such systems thus do provide control over particular network peripherals such as printers and disk drives, but they do not provide control over devices which they do not support. In addition, these systems do not provide any fundamental control over the access to the media itself.
Yet another solution is to physically isolate the stations, which of course, prevents any packet traffic between them. Communications between two or more LANs can then be enabled on a controlled basis, by employing interconnection devices such as routers or bridges. However, stations on the same LAN will still have complete access to one another, and thus, this approach only partially solves the difficulty. Additionally, the use of bridges and routers unnecessarily complicates the physical configuration of the network.
What is needed is a way to provide access control within a peer-to-peer communication network without the use of encryption, active participation in security protocols, operating systems, or physical isolation. The technique should not require participation by the network stations; in fact, it should be invisible to them. The technique should also not require reconfiguration of the network, and should be simple and inexpensive to implement. It is also desirable to accomplish this in such a way that the unauthorized users do not know they are being controlled.